Oxygen sensors are used for inter alia the measurement and control of the air-to-fuel ratio in combustion systems such as automobile engines and gas-fired boilers. The sensor is situated in the exhaust gas and measurement of the oxygen content of the gas enables the efficiency of combustion and control of emissions to be optimised.
Typically an oxygen sensor comprises a substrate of alumina, a first electrode serving as a cathode residing on the substrate, a solid metal oxide oxygen ion conductor electrolyte residing on the cathode and a second electrode serving as an anode residing on the electrolyte. Typically the electrolyte is of zirconia while the electrodes are of platinum.
At present oxygen sensors of the type described comprise discrete electrode and electrolyte components. These sensors are relatively expensive however and to reduce the costs attempts have been made to fabricate the electrodes and the electrolyte as printed layers on the substrate. However, the sensors produced have suffered from a lack of adhesion between the platinum cathode and the electrolyte in particular and also between the platinum anode and the electrolyte as well and so printing of the sensors has not been a popular technique.